Why won't my iPad stay charged when using a USB charger?

Our testing has shown that if you have screen brightness turned up to maximum, that has a very big impact on battery life and the ability for a charger to make headway on battery charging when ForeFlight Mobile is running.

If you reduce your brightness setting under MORE > SETTINGS, even a little (say by 20% to 40% of the slider), then that will have a significant impact on how fast the battery power is consumed. That may allow the charger to either increase the battery percentage or at least reduce the rate of power consumption.